Old Ladies and Evolution

I think of most human activity in evolutionary terms. Our evolutionary past killed off any of us who didn’t act a certain way and encouraged those of us who did.

I was chatting with a friend yesterday, who said that she tended to think that without God (and fear of retribution), human society would fall apart. She asked my theory.

Of course, my answer was evolution. In our evolutionary past, those not-quite-humans who didn’t stick with the pack either got killed before reproducing, or evolved into something else. Those who tended to be more social mated with each other, producing offspring who tended to be more social. And so on, and so on until we evolved to MySpace.

For years, people have been considering the evolutionary reasons behind menopause, and the degradation of fertility leading up to it.

Is it a matter of being a waste to get pregnant when you’re too old and weak to carry a baby? That sounds reasonable, but on its own, it’s not an evolutionary force. That is, evolution doesn’t care whether you stop having babies because of menopause, or because you die having the 6th one. You’ve had your 5, and you’ve passed on your genes.

Besides, most other animals don’t bother with the whole thing. They go on being at least somewhat fertile until the day they die. What’s going on?

Apparently, the theories break down into three main groups:

1. Menopause is an adaptation that allows women to be better mothers to the children they already have. This increases the odds that those children will survive to pass on their genes, thus also passing on mom’s.

2. Menopause is an adaptation that allows women to be better GRANDmothers, with the same benefits as above. The main difference is that grandmothers can be off foraging for food while mom is breast-feeding.

3. Menopause isn’t an adaptation on its own, but is a side-effect of some other adaptation. Maybe it’s just another part of the general falling-apart we do as we age. (Though some research suggests that, even if it’s a side-effect of aging, it could be timed to help with raising the young-uns.)

Number three is completely unsatisfying, so it’s probably the right answer. I doubt anyone wants to read more, but there’s a slightly out-of-date collection of research articles posted at Menopause and Beyond.